This invention is concerned generally with bobbin type transformers, and, more particularly, with compact transformer bobbin assemblies which meet the International Electrotechnical Committee (IEC), International Committee on Rules for the Application of Electrical Equipment (IEE), Verband Deutscher Elektrotechniker (VDE), and British Standards Institute (BSI) standards.
Manufacturing transformers to meet these standards in the past has typically resulted in transformers that are costly to produce since they are labor-intensive. The older tape wound insulation approach resulted in very thick tape layers to provide the necessary creepage and clearance distances (i.e., creepage distance is the shortest distance along the intermediate surface between two windings or leads, whereas clearance distance is the shortest distance either through air or over the intermediate surface or any combination of the two), and high voltage insulation that these standards call for, increasing the size of these transformers and the labor for manufacturing them unnecessarily. A second approach of the prior art is a bobbin and shield arrangement wherein the individual bobbins were aligned linearly with a shield between each bobbin to provide the required minimum creepage and clearance distances and high voltage insulation. Transformers of this configuration are also bulky and heavy as a result of the large amount of steel necessary for laminations since the elements are arranged linearly. The linear arrangements of the elements also result in an inefficient transformer since a large amount of the energy goes into stray fields which were not coupled to the other windings.
It would be desirable to design an isolating type transformer that meets the IEC, CEE, VDE and BSI standards which is not as bulky, is not as labor-intensive to manufacture and more efficiently couples the energy between each of the various windings. The present invention disclosed herein represents such a transformer.
In accordance with the preferred embodiment, the bobbin assembly of the present invention consists of three pieces, two primary bobbin pieces and a secondary bobbin piece. The secondary bobbin piece is designed to provide the necessary creepage and clearance distances between the individual primary windings through the inclusion of a web within its central opening midway between its two exterior surfaces and stepped external flanges. Also, the lead wire spacing of the primary leads is maintained by passing these leads through the holes provided in the outer flange of each of the primary bobbin pieces. When assembled, the two primary bobbin pieces nest within the interior opening within the secondary bobbin piece from opposite sides.